The black damping material is mostly 1/8" SoundCoat from Sonic Craft plus some EAR TED from Michael Percy I already had.
I love the way these sound--VERY spacious and big, very transparent, and with the BEST bass I've EVER heard...anywhere. I'm still in process of balancing the treble, and I have to admit that the quality of the sound in the treble isn't as high as it is in the other 7 octaves.